Add removeAlpha op, removes alpha channel if any #1248

docs/api-channel.md

@@ -1,5 +1,21 @@
 <!-- Generated by documentation.js. Update this documentation by updating the source code. -->
 
+## removeAlpha
+
+Remove alpha channel, if any. This is a no-op if the image does not have an alpha channel.
+
+### Examples
+
+```javascript
+sharp('rgba.png')
+  .removeAlpha()
+  .toFile('rgb.png', function(err, info) {
+    // rgb.png is a 3 channel image without an alpha channel
+  });
+```
+
+Returns **Sharp** 
+
 ## extractChannel
 
 Extract a single channel from a multi-channel image.

docs/api-input.md

@@ -79,6 +79,7 @@ A Promise is returned when `callback` is not provided.
     -   `maxX` (x-coordinate of one of the pixel where the maximum lies)
     -   `maxY` (y-coordinate of one of the pixel where the maximum lies)
 -   `isOpaque`: Value to identify if the image is opaque or transparent, based on the presence and use of alpha channel
+-   `entropy`: Histogram-based estimation of greyscale entropy, discarding alpha channel if any (experimental)
 
 ### Parameters
 

docs/changelog.md

@@ -6,6 +6,9 @@ Requires libvips v8.6.1.
 
 #### v0.20.6 - TBD
 
+* Add removeAlpha operation to remove alpha channel, if any.
+  [#1248](https://github.com/lovell/sharp/issues/1248)
+
 * Expose mozjpeg quant_table flag.
   [#1285](https://github.com/lovell/sharp/pull/1285)
   [@rexxars](https://github.com/rexxars)